The Hauraki Gulf is struggling to keep up with the effects of population growth and climate change, a new report found.
The State of Our Gulf report, released Friday, highlights a number of problems faced by the gulf - with poor fish and marine life stocks at the top of the list.
"I often hear fishing people say, 'But there's plenty of fish, I'm still catching them,'" Hauraki District Council Mayor John Tregidga and chair of the Hauraki Gulf Forum, said at the report's official release.
"And there are in some areas. But if we talk about the total gulf catchment, we know it's coming under stress."
He said some species - such as snapper and crayfish - now only have 20 percent the stock they used to, and it's not sustainable.
"We're not catching less fish, we're not milking less cows and we're certainly not building less homes. Pressure on the gulf is increasing, and investment and infrastructure and new policy directions are not keeping pace."
One problem was fishers' habit of throwing the little ones back, and keeping the big ones - because it's the big ones that are sexually mature and producing offspring.
"Sometimes I think we should be catching the small ones, and throwing the big ones back."
Other pressures on the gulf noted in the report come from increasing amounts of chemicals and pathogens (thanks to stormwater overflows, septic tanks and livestock), the spread of mangroves and other pests, increased littering and the growth of recreational facilities.
"Since the last report in the last three years we've had a number of new marinas, a number of new boat ramps and some 12 private jetties. This is all putting pressure on the Hauraki Gulf," said Mr Tregidga.
The Hauraki Gulf Forum is calling for authorities - central and local government, as well as iwi - to work together on a "renewed, integrated programme of action".
"An integrated approach has remained elusive despite the efforts of the Hauraki Gulf Forum over 17 years."
Obstacles include the technical complexity of measuring the state of the gulf, commercial imperatives, conflicts in legislation, the costs, and the slow pace of change at large institutions.
"I [enjoyed the gulf] as a young person - sailed on it, fished on it, have enjoyed it ever since - but we need to understand the numbers that are actually fishing, enjoying it do have an adverse effect," said Mr Tregidga.
"I'm not saying it should stop, but what I am saying is we need to start telling people that you need to think about what you're doing on the gulf and enjoying it to ensure that it's there for the future. It's a bit of a fine balance."
One that climate change could ruin if changes aren't made.
"The Hauraki Gulf will become warmer and more acidic. Risk associated with invasive species will increase. The pace of change is outstripping the ability of our current management frameworks to respond effectively."
Not all bad news
Some positive changes on the gulf were noted, including a reduced number of Bryde's whales being hit by ships. Up until four years ago, on average around two were hit and killed every year - but rather than wait for legislators to catch up, he went straight to those causing the deaths.
"We sat down and talked it through with [the shipping industry]," said Mr Tregidga.
"Today I can tell you we've had one in the last four years, and virtually all ships are travelling at 10 knots... the chances of a whale strike is minimal."
He also had praise for Auckland Council's SafeSwim initiative, which lets the public know which beaches are safe to swim at, and which are contaminated.
"It's only when we face up to these issues that we can build a case for our communities to invest in change."
And farmers were praised for taking efforts to reduce nutrient runoff into streams that flow into the Hauraki Gulf.
"People need to understand it is all interconnected."